This invention relates to a blood pump applicable to an artificial heart.
Recently, the development of an artificial heart has been made aiming at the cardiac assistance which is expected to function temporarily in place of the natural heart of a patient at the open-heart surgery. Requirements for the artificial heart call for as follows:
(1) the shape of the artificial heart should be essentially compatible with the body;
(2) the blood stream should have the least stagnant flow and the sufficient attention should be paid to the thromboregistancy.
(3) the flow-resistance should be small to maintain the sufficient blood flow by the normal venous pressure;
(4) the volume of the ventricle of the artificial heart should be pertinent to the patient's body;
(5) the artificial heart should be easily attachable to and detachable from the patient's body;
(6) the fatigue of the constituent materials of the artificial heart should be small and the sufficient durability should be guaranteed;
(7) the design of the artificial heart should be made considering the least hemolysis; and
(8) the excessive negative pressure should be avoided at the ventricular distole period.
Among these requirements, (2) and (6) are the most important. The antithrombus property is influenced by hydrogynamic factors such as the design of the blood pump and roughness of the blood-contact-surface, the physical, chemical and electrical properties of the constituent materials of the artificial heart, the environmental manufacturing conditions, and so on. Especially, the design of the pump is important. Even a little modification of the shape critically influences on the blood-flow pattern in the pump. It may cause troubles in the actual long operation. The thrombosis is considered to be formed mainly due to the blood-stream conditions in the pump, particularly to the stagnation in the blood-stream. The thrombosis is complicatedly influenced by the velocity of the blood-stream, the main residence time of the blood in the pump, the shear rate of the blood at the contact-surface of the pump, etc.
For the practical use of the artificial heart, it is indispensable that the blood flux out of the pump and the pressure wave form thereof should be enough to maintain the circulation of the blood so that whole body of the patient. In other words, to function as the artificial heart, the blood pressure curves caused by the blood pump must resemble to those of the natural heart as closely as possible. Ideally, the former should be the same as the latter. When the difference of the blood pressure curve between the pump and the natural heart becomes larger than the critical level, patient's body is no longer adapted to the circumstances. In this case the patient's condition becomes bad. The most important thing to keep in mind is that the patient's conditions, who is supposed to use the artificial heart, are usually very bad. Therefore, the patient reacts so sensitively to a small difference from the natural heart, which may often become fatal.